Not technically melee, but I really like "throw a rock at it" as a solution:
Lolth Touched Half Minotaur Goliath Fighter 4/Mountain Rage Barbarian 1/Hulking Hurler 3/War Hulk 1 (ECL 12, or 11 with paydown)
Racial Stats: +22 Str, -4 Dex, +14 Con, -2 Int, +2 Wis, +4 Natural Armor, Large, Track Feat, Darkvision 60', Scent, Movement 40', +2 on Search, Spot, and Listen, +4 Hide and Move Silently, Immune to Fear, 1d8 Gore, Always know north and +4 to escape Maze, Mountain Movement, +2 Sense Motive
Stats (32 point buy): Str 48, Dex 12, 28 Con, 6 Int, 10 Wis, 6 Cha, Initiative +14 (Str 54 and Con 32 during rage)
Feats (2 Flaws): 1: Point Blank Shot, Power Attack, Weapon Focus (Rocks), Far Shot 2: Brutal Throw 3: Cleave 4: Weapon Specialization (Rocks) 6: Improved Initiative 9: Ranged Weapon Mastery: Bludgeoning
Hurl Tricks: Overburdened Heave (can throw up to medium load), Meteor Strike (Deals extra damage equal to twice strength bonus on hit)
Gear: Belt of Giant Strength +4 and Battle (28kgp), +1 Morphing Shuriken of Warning and Initiative (646 gp, turned into knee blade)
Throw Rocks during rage: +29 for (599d6+81), range increment 70',
To avoid the explosion, he's going to throw his rock at the Balor from 130' away (-2 penalty to hit for range) while raging (makes him huge). His medium load in Mountain Rage is 119296lbs, so that's the weight of the rock he throws. In case he misses, he uses his Belt of Battle to throw a second rock. Hopefully his initiative of +14 is sufficient. I know, this is silly, but I really wanted to just squish the big guy with a rock. Honestly he doesn't really need so many Hulking Hurler levels (obviously the damage is plenty without Meteor Strike or Overburdened Heave) or the War Hulk level, but he did need to get Ranged Weapon Mastery to actually hit at such long ranges (I could have been even more silly and used Martial Monk 2 for the RWM and Weapon Supremacy).
JaronK